17-alpha hydroxyprogesterone (alternatively hereinafter referred to as 17-hydroxyprogesterone or “17HP”) is a C-21 endogenous steroid hormone produced during the syntheses of glucocorticoids and sex steroids. Like progesterone, 17HP is a natural progestagen. It has been isolated from both adrenal glands and corpora lutea. Esters of 17HP are reported to have progestogenic effects and hence, can be used for indications related to pregnancy support as well as non-pregnancy support in both pre- and post-menopausal women. It is reported that 17HP, without esterification, has no progestational activity. However, the synthetic esters of 17HP such 17-hydroxyprogesterone acetate or 17-alpha-hydroxyprogesterone caproate (also referred hereafter as 17 hydroxyprogesterone caproate or 17 HPC) have been shown to exhibit marked progestational activity when administered intramuscularly in animal experiments. 17-Hydroxyprogesterone caproate is a commonly used progestin available for intramuscular injection to prevent Preterm Birth (alternatively hereinafter referred to as “PTB”). This synthetic caproate ester is reportedly inactive when given by mouth but works as a long-acting progestin when administered intramuscularly. The metabolism of 17HP and the metabolism of 17-hydroxyprogesterone caproate in the human female are not yet fully established. Data from humans and animals indicate that intramuscularly administered 17-hydroxyprogesterone caproate has more potent progestational effect on endometrium and is longer lasting than progesterone (alternatively hereinafter referred to as “P”). This may be due to more avid binding of 17-hydroxyprogesterone caproate to the progesterone receptors (alternatively referred to hereinafter as “PR”) and placental glucocorticoid receptors (alternatively referred to hereinafter as “GR”) that could prevent an increase of placental corticotropin releasing hormone which is associated with onset of labor. 17-hydroxyprogesterone caproate is reportedly effective in providing luteal support in patients undergoing IVF-Embryo Transfer Cycles.
PTB is medically defined as delivery from 20 to 36 weeks of gestation. According to the 2009 Center for Disease Control Report, PTB occurs in about 12.3% of births in the US alone translating to about half a million PTBs annually. Spontaneous PTB accounts for approximately 70-80% of PTB. Of all the pregnancies in the US, one out of every eight live-born infants is born preterm representing an increase of >18% since 1990. Late pre-term birth between 35-36 weeks of gestation contributes to more than half of all PTBs. PTB is the primary cause of neonatal morbidity and mortality. Mortality risk is three fold higher at 35-36 weeks and morbidities such as respiratory distress requiring oxygen, temperature instability, hypoglycemia, jaundice, attention deficit disorders, cerebral palsy, developmental delay, etc. are quite common. PTB related time and costs in intensive care are a major health, social and economic issue with an average cost of PTB delivery amounting to up to 10× that of normal delivery.
Major risk factors implicated in PTB are as follows: History of previous spontaneous PTB (past obstetrics history), cervical length (<2.5 cm at mid pregnancy), presence of fetal fibronectin in vaginal secretions; multiple gestation, low maternal Body Mass Index (BMI), maternal race; maternal age (<17 and >35 years), and smoking. The prior history of at least one PTB is a good indicator of future occurrence potential with 17-50% recurrence potential and 28-70% recurrence potential with two previous PTBs. Benefits of prolonging pregnancy to full term with therapeutic intervention include improved child survival as a function of gestational age, and reduced neonatal hospital stay.
Intramuscular injection of 17-hydroxyprogesterone caproate is available for reducing the risk of PTB in women with singleton pregnancy and history of single spontaneous PTB. The injection marketed as Makena® (250 mg 17-hydroxyprogesterone caproate in 1 mL) mandates regular visits to the doctor's office, as the typical treatment cycle consists of 16-20 weeks of injection repeated every week. This therapy regimen could result increasing the patient's distress and/or anxiety in addition to increasing the repeated travel risks for the patient and fetus. The injection therapy's interferences with the personal and family activities and disruption in professional life are also a major disadvantage.
In addition, adverse events with injection of 17-hydroxyprogesterone caproate (e.g. Makena®) at once weekly (every 7 days) the injection site reactions (˜45%) such as urticaria, pruritis, swelling, nodule formation and pain at the site of injection have been reported as significant.
Esters of hydroxy progesterone such as acetate, caproate, undecanoate are more lipophilic than hydroxy progesterone. The active substance (17-hydroxyprogesterone caproate) in Makena® is known to be extremely insoluble in water (<20 ng/mL), and very lipophilic with ClogP of about 5.7. Moreover, 17-hydroxyprogesterone caproate has the potential to be metabolized in the presence of fetal and adult hepatocytes and is a substrate for cytochrome inactivation such as CYP3A4 which is overly expressed in pregnant women (˜40% upregulation). Due to its extremely low water solubility and a potential to be susceptible for first pass hepatic inactivation oral delivery of long chain esters of 17HP has remained a challenge. It is reported that there is no oral activity with 17 hydroxyprogesterone caproate, an ester of 17 HP, (Saxton D J et. al. Reproductive Biology and Endocrinology 2004, 2:80; Greene M F, NJEM 348:2453-2455). This could be likely due to very poor or no oral bioavailability of 17 HPC. Although much desired, to date the development of an orally active composition of long chain ester of hydroxyl progesterone remains a significant unmet need. In addition, development of dosage forms that enable administration of lesser number of dosage units per dose and/or at reduced frequency per day is most often desirable.